"Just use transactions" is not sufficient to solve concurrency problems under load.
You didn't recommend going away from transactions anywhere that I saw, just tuning them. Thus, you seem to agree with me.
As for my parting comment about whether you had relevant experience, that is an educated guess at best, which you could easily confirm or deny.
I have worked on heavy-transaction systems. But, I will admit that most of my projects tend to be management information and decision support systems rather than high-volume transactions.